You can also look up the gm of the nuvistors and get a reasonable match to a
fet as well.
Don
----- Original Message -----
From: "J. Forster" <j...@quik.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Sunday, May 02, 2010 9:23 PM
Subject: Re: [time-nuts] Nuvistors and FETs...
Interesting idea. In fact, the later versions of the loop used FETs in
place of Nuvistors. I've not compared the circuits.
Because the thing is only 60 KHz, the change in grid/gate capacitance may
not matter much. There may be some mounting and stability issues though
because the plate caps were on the opposite side of a metal shield from
the grids.
-John
================
For what it may be worth, I've swapped Nuvistors out with FETS. I
see from the schematic that the Nuvistors are running on 35
Volts. It would be simple to drop the 35 Volts to 12 or 8 Volts with
a 3 terminal regulator in the receiver. If desperation sets in, try
stuffing N-Channel FETs in place of the Nuvistors. The gate is the
grid, the drain is the plate, and the source is the cathouse. Since
the FETs are usually pretty low in capacitance you may need to shunt
the tuned circuit/s with a small piston type capacitor. In one low
Voltage preamp circuit I used a National U-310. In another one, a
Nems Clark receiver, I replaced the two RF front end ceramic triodes
stages that ran on 150 Volts with two U-310's and rewired the plate
supply to run off of the 12 Volts already in the receiver. This made
for a low noise, very sensitive front end. All I needed to do was
add a small quartz piston capacitor to bring the tracking in at the
high end and the bottom end fell right end. If you can make that
work, you'll never have to replace those pesky wittle Nuvistors again.
Burt, K6OQK
From: paul swed <paulsw...@gmail.com>
Subject: Re: [time-nuts] 6CW4 Nuvistors on eBay...
Indeed there are.
And even 7587s thats the TRF frontend. In one of the units V3 appears bad
all Rs are good voltage high on plate, 0 cathode current. But oddly when
I
swap v1 into position same effect so somethings odd. Or my methods not
correct.
The other units working. Had to replace a shorted 6.2 V zener.
The 100 kc vco /lock osc is awful touchy.
Pretty amazing the units pretty hot sensitivity wise -80 dbm.
Interesting afternoon. Way in the deep corner of the basement I think I
may
have a nuvistor or two. Time to see what they are.
On Sun, May 2, 2010 at 4:14 PM, Burt I. Weiner <b...@att.net> wrote:
>
> For what it's worth, I just took a look and found a bunch of 6CW4's on
> eBay. See:
Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California U.S.A.
b...@att.net
K6OQK
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